Process of tempering gold and silver alloys



Patented Aug. 23, 1938 UNITED STATES PROCESS OF TEMPERING GOLD AND SILVER ALLOYS Claude H. Coleman, Fail-mead, Calif.

No Drawing. Application April 21, 1938, Serial No. 203,465

'3 Claims. (01.148-131) This application constitutes a continuation in part of application, Ser. No. 135,350, filed April 6, 1937, and the invention herein set forth relates to a process for hardening alloys of gold and silver with non-ferrous metals and has for its object to give such alloys a substantial degree of hardness to better adapt them to commercial uses and to temper the alloys whilst avoiding the formation of oxides upon the surface of the metal during the tempering process.

With these objects in view, the present invention consists in a process for increasing the hardness of alloys of gold and silver with non-ferrous metals which consists in first reducing the temperature of the alloy from a normal temperature which approximates average room temperature to approximately the freezing point of water, then immersing the chilled alloy in a hot bath consisting of one of the group comprising tallow, mineral oil, petroleum jelly, the temperature of which is at least 380 F., and maintaining the alloy therein for a sufficient time to permit the heat to penstrate through the alloy, then immersing the alloy in a boiling soap solution for a period sufiicient to cleanse the oil therefrom, and finally removing the alloy from the soap solution, drying the same and allowing it to return to room temperature.

In general, the present gold and silver alloy tempering process is carried out as follows: The

3 piece of metal (the alloy) which is to be tempered,

is first reduced from a normal temperature which approximates average room temperature to or slightly below the freezing point of water and is then immersed in a bath of beef tallow which has. been raised to a temperature of approximately 380 F., the immersion being for a period of approximately twenty seconds to permit the heat to penetrate through the alloy. Immediately following this immersion for the time period stated, the

40 metal is transferred to a solution ofv soap which is made fairly strong and which is kept at the boiling point. The metal alloy is allowed to remain in this solution for approximately twenty seconds to cleanse the oil therefrom. Following this last step, the metal is removed and thoroughly dried and allowed to cool to a temperature of between and F., but is not necessary to go below 60. It is then subjected to a second chilling step and is reduced to a temperature of ap- 50 proximately 10 below zero. Any suitable means may be employed for effecting the chilling of the .metal, such as placing of the same in a suitable refrigerating chamber or placing it between bodies of solidified carbon dioxide, commonly 55 known as dry ice or any other method of freezing.

When the desired temperature has been obtained in the metal, it is then immersed in the hot tallow solution, the temperature of which has 0 been raised to approximately 400 F. The second immersion in the hot tallow is for approximately twenty seconds and the metal is then introduced into the boiling soap solution for twenty seconds, after which it is thoroughly dried and retained at the temperature above set forth until the process can be carried forward to the next step. With each repetition of the three steps of chilling, immersion in hot tallow, and then in the soap solution, the temperature of the tallow is 400 F. Then continue to repeat this last mentioned process until the desired degree of hardness in the metal is obtained.

In order to obtain a certain degree of hardness, the foregoing steps are repeated every four hours, when a refrigerating chamber is used, for a period 15 of from twenty to twenty-one days and the metal begins to harden before the end of this time, but the process may be continued for the full length of time or longer or until the maximum degree of hardness is obtained. This method contemplates 20 the use of a freezing unit of a standard commercial refrigerator. When dry ice is used, the desired temperatures are reached much sooner and, therefore, the process can be repeated at more frequent intervals. The temperature of the tallow should not go beyond 390 to 400 F.

The reaction occurring in rapidly changing the metal from the chilled condition to a highly heated condition by immersion in hot tallow, has the effect of hardening and toughening the metal 0 and at the same time keeps the metal out of contact with the air so that it will not become oxidized during the heating process.

The hot soap solution cleans out the pores of the metal and removes the tallow therefrom so that the heat of the metal will be more rapidly dissipated during the chilling process and also prevents oxidation.

While in the foregoing statement of the process it is stated that the immersion of the metal in the 54 tallow solution is for approximately twenty sec onds, this time may be changed slightly to suit the quantity or thickness of the metal being treated.

If a small or thin piece of gold or silver alloy is being hardened, the immersion need not be for 4 longer than ten seconds when the tallow is at a temperature of 400 F., while a heavy or thicker piece would require a longer time in the carrying out of the freezing process and in immersion in the tallow. .5

In addition to cleaning the metal, the immersion of the same in the boiling soap solution, effects a gradual reduction of the temperature While keeping the metal out of contact withthe air. 555

By the foregoing process bodies of gold and silver alloys have been given a degree of hardness sufficient to suit the same for use as jewelry, chimes, bells, and also gold and silver coins. One

' twenty-dollar piece was actually raised scale 0 F, Rockwell hardness. The process may be continued for the length of time specified or longer or until the desired degree of hardness has been obtained.

Mineral oils, petroleum jelly, vegetable oils and other animal fats can be used, but it is preferred that beef tallow be used because it will carry or retain a higher temperature than mineral oils and it will heat the metal moreevenly, leaving it tougher and with a finer grain.

The soap solution may be made from any suitable soap, and it is preferred that a. solution be made which has a density of approximately 1.009.

One brand of soap bought in the market which has been employed in connection with this process with satisfactory results was found to contain upon analysis:-

, Per cent Moisture 2 6.25 Total alkali (NazCOa) 23.85 Total fatty matter 70.60 Free caustic alkali (NaOH); 0.18 Free fatty acids None The fatty matter of this soap is cotton-seed stearine.

Specific gravity at 100 C .867 Solidifying point 30 C.

The following are examples of results obtained under test:

1. An alloy comprising:

Gold 60% (pure) Copper 1 25% (99.8% pure) Silver 15% (pure) was found to test 6.0 in hardness Rockwell G scale. After 52 repeated immersions the alloy tested 73.3 in hardness on the same scale.

2. An alloy comprising:

Gold 75% (pure) Silver 5% (pure) Copper 20% (99.8% pure) was found to test 81.6 in hardness Rockwell B scale. After 68 repeated immersions the alloy tested 93.7 on the same scale.

3. An alloy comprising:

Per cent Gold 51 Copper 40 Silver 9 was prepared and under test. for hardness on the Rockwell F scale showed as an average of three tests a hardness of 83.7. This alloywas then subjected to forty repetitions of the treatment outlined and then showed as an average of three tests made, a hardness of 85.7 Rockwell F scale. Forty more repetitions of the process were then made in connection with this particular alloy, making in all eighty treatments and this alloy then showed as an average of three tests a hardness of 9 1.0 Rockwell F scale.

4. An alloy comprising:

Per cent Gold 91 Copper 8 .Silver 1 was prepared and showed as an average of three tests a hardness of 67.7 Rockwell F scale. After subjecting this alloy to forty repetitions of the herein described process, it showed as an average of three tests made thereon a hardness of 70.7 Rockwell F scale. After subjecting this alloy to forty more treatments according to the process outlined, making a total of eighty treatments given, an average of three tests showed a hardness of 76.7 Rockwell F scale.

All of the alloys set forth, were subjected to a spectrographic analysis before and after sub- J'ecting them to the treatments specified and no change in purity, composition, grain size or molecular orientation of any one of the alloys could be detected.

What is claimed is:

1. The improved process of hardening an alloy consisting of gold ranging from 51% to 91%, copper from 40% to 8% and silver from 9% to 1%, which comprises the steps of first reducing the temperature of the alloy from a normal temperature which approximates average room temperature to at least the freezing temperature of water, then immersing the chilled alloy in a bath of tallow having a temperature of at, least 380 F. and maintaining the alloy therein for at least 20 seconds, then immersing the alloy in a boiling soap solution for at least 20 seconds, removing the alloy from the soap solution, drying the same and allowing it to return to room temperature, and repeating the process as required to obtain a desired hardness, the reduction of the temperature of the alloy on the second and subsequent repetitions being to approximately 10 F.

2. The improved process for hardening an alloy consisting of approximately gold, approximately 25% copper and approximately 15% silver, which comprises the steps of first reducing the temperature of the alloy from a normal temperature which approximates average room temperature to at least the freezing temperature of water, then immersing the chilled alloy in a bath of tallow having a temperature of at least 380 F. and maintaining the alloy therein for at least 20 seconds, then immersing the alloy in a boiling soap solution for at least 20 seconds, removing the alloy from the soap solution, drying the same and allowing it to return to room temperature, and repeating the process as required to obtain a desired hardness, the reduction of the temperature of the alloy on the second and subsequent temperature which approximates average room temperature to at least the freezing temperature of water, then immersing the chilled alloy in a bath of tallow having a temperature of at least 380 F. and maintaining the alloy therein for at least 20 seconds, then immersing the alloy in a boiling soap solution for at least 20 seconds, removing the alloy from the soap solution, drying the same and allowing it to return to room temperature, and repeating the process as required to obtain a desired hardness, the reduction of the temperature of the alloy on the second and subsequent repetitions being to approximately l0 F.

CLAUDE H. COLEMAN. 

